Back-pressure turbine



BACK rnnssvxs wanna Filed lurch 3, 1927 Jn/en/of:

ffnr/ e y K. FREY 1,750,262

Patented Mar. 11, 1930 UNITED STATES PATENT OFFICE KARL FREY, OF BADEN, SWITZERLAND, ASSIGNOR TO AK'IIENGESELLSGHAFT BROWN BOVERI 8t CIE, OF BAD'EN, SWITZERLAND,A'JOINT-STOCK COMPANY OF SWITZER- LAND BACK-PRESSURE TURBINE Application filed March 3, 1927, Serial No. 172,543, and in Germany March 5, 1926.

This invention relates to steam turbines of the type designed to work against back pressure, and in which it is customary to control the admission of steam by means of a governor responsive to the said back pressure.

The general object of the invention is to provide a turbine of this type which can be run light, i. e. during times when the demand for process steam has fallen to zero, without 10 danger from overheating.

Another object is the provision of means for securing this object which are perfectly automatic and reliable in action.

A further object is the provision of means for securing this object in the most simple manner, consistent with reliability.

Other and further objects will be pointed out or indicated hereafter, or will appear to one skilled in the art on an understanding of the present invention or its employment in practice. 7

In the drawing forming part of this specification, I show several arrangements in which the invention is embodied, but it is to be understood that these are here presented for purposes of illustration only, and are not to be accorded any interpretation calculated to limit the claims short of the true and most comprehensive scope of the invention in the art. V

In the drawing, Fig. 1 is a cross-section of the top half of a back-pressure turbine embodying the invention, and

Figs. 2 and 3 are similar views showing modified arrangements.

When a back-pressure turbine is operated on a very small load there is excessive friction between the steam and the revolving blades which can easily give rise to dangerous over- 40 heating. The efiect is very considerably en hanced when the back-pressure is high. As the demand for process steam which is being taken from such a turbine falls, the back-pressure governor reduces the admission of steam to the turbine until eventually, if the demand falls to zero, no steam will be admitted at all and the turbine, if coupled to an electric generator, will be driven by the latter, the generator acting as a motor. In such circum stances excessive and dangerous overheating of the turbine is bound to occur.

To prevent such overheating, even when the demand for process steam has fallen to zero, I arrange that a certain quantity of steam, sufiicient to prevent overheating, shall be admitted to the turbine at all times; that is to say, the admission of such steam is to be entirely independent of the back-pressure governor which normally controls the whole admission. With such an arrangement a certain quantity of steamwill always be flowing through the turbine even when the backpressure governor owing to the reduction to zero of the demand for process steam, has closed all the valves under its control. This minimum quantity of steam will be automatically discharged through the safety valve with which all back-pressure turbines are fitted and if desired it may be led off for feed heating purposes. Even if this steam is allowed to escape, however, the method is preferable to prior art practice in which a complete interruption of the demand for steam means that a certain quantity at least must be blown off b the boilers, while at the same time the winc age losses in the turbine are supplied from the mains (generator running as motor).

The nature of the invention will be ascertained in more detail in the examples shown in the drawing. Referring to that illustrated in Fig. 1, let it be understood that the numerals 3 and 4 designate oil relays operating nozzle valves which control the admission of steam to the nozzle groups 8 and 9. The numeral 5 designates a back-pressure governor controlling the aforesaid oil relays. Thus when the back-pressure increases, as will occur for example as the demand for process steam falls, the diaphragm of the back-pressure governor will be depressed, the oil escape valve will be opened, and the oil relay pistons will be forced downward by their springs so as to close the nozzle valves and reduce the admission of steam.

The numeral 1 designates an oil relay which operated the nozzle valve controlling the nozzle group 7. This oil relay is not controlled by the back-pressure governor but by the ordinary speed governor 2. This latter will only be effective in the event of an excessive rise in the turbine speed. Under normal conditions the speed will be maintained constant by the generator and the nozzle group 7 will always remain open so as to admit sufficient steam to the turbine to prevent overheating.

In the arrangement illustrated in Fig. 2 the minimum quantity of steam necessar to prevent overheating is admitted througi a special nozzle 7, which is independent of any kind of governor control. Reference to the drawing will show that this nozzle is placed immediately after the main steam-supply valve 6 and consequently is always under steam except when the turbine is shut down altogether. Such an arrangement is permissible owing to the fact that the quantity of steam necessary to prevent overheating is usually less than the quantity required to run the turbine light and consequently there is no danger of the turbine speeding up under the minimum quantity admitted by nozzle 7 Hence this nozzle may be ungoverned.

In the arrangement shown in Fig. 3 the steam necessary to prevent overheating is admitted to the nozzle group 8 through a bypass arrangement 10. This by-pass may be adjustable as shown so that the quantity admitted may be adjusted to the value giving the best results. It will be seen that even if the nozzle valves 3 and 4 are closed a certain flow will always take place through the bypass 10 and therefore no overheating can occur.

From the foregoing it will be seen that in the present improved construction, the turbine casing is provided with a plurality of consecutively arranged steam-supply chambers partitioned one from the other, these being chambers 11, 12 and 13 in Fig. 1; chambers 14:, 15 and 16 in Fig. 2; and chambers 17 and 18 in Fig. 3. Such chambers have a common steam-supply chest 19, a main steam-supply controlling valve 6 being interposed between chest 19 and the adjacent endmost steam-supply chamber; the latter being chamber 11 in Fig. 1. chamber 14 in Fig. 2, and chamber 17 in Fig. 3.

Valve means; such as valves 20 and 21 in Fig. 1, valves 22 and 23 in Fig. 2, and valve 2-1 in Fig. 3; are associated respectively with steam-supply chambers 12, 13, 15, 16 and 18, and control steam flow thereinto from steamsupply chest 19 by way of main valve 6.

The oil relays, such as relays 3 and 4: in

Figs. 1 and 2 and relay 4 in Fig. 3, constitute means responsive to high and low back'pressure conditions of the turbine and which operate at such conditions to effect closing and opening movements respectively of the associated valves.

It will be seen, further, that the end-most steam-supply chambers 11, 14C and 17 are in direct communication at all back-pressure conditions with steam-supply chest 19 by way of main valve 6.

The invention is also readily applied to turbines which are not provided with a plurality of valve controlled nozzle groups; to pure reaction turbines for instance. In such a case the bypass could be arranged to lead the steam from the boiler side of the main admission valve direct to the first row of blades. Alternatively this valve can be fitted with a stop to prevent complete closure or with an internal port permitting the desired quantity of steam to pass at all times.

lVhat I claim is:

1. In steam turbine apparatus, a turbine casing provided with a plurality of consecutively arranged steam-supply chambers partitioned one from the other, a steam-supply chest common to said chambers, a main steam-supply controlling valve interposed between said steam-supply chest and one of the end-most of said steam-supply chambers, valve means associated with the other of said chambers for controlling steam flow thereinto from said chest by way of said main valve, and means responsive to high and low back-pressure conditions of said turbine and being operable at such conditions to effect closing and opening movements respectively of said valve means, said end-most of said steam-supply chambers being in direct communication at all back-pressure conditions with said steam-supply chest by way of said main valve.

2. In steam turbine apparatus, a turbine casing provided with a plurality of consecutively arranged steam-supply chambers par titioned one from the other, a steam-supply chest common to said chambers, a main steam-supply controlling valve interposed between said steam-supply chest and one of the end-most of said steam-supply chambers, valve means associated with the other of said chambers for controlling steam flow thereinto from said chest by way of said main valve,means responsive to high and lowbackpressure conditions of said turbine and being operable at such conditions to effect closing and opening movements respectively of said valve means, said end-most of said steamsupply chambers being in direct communication at all back-pressure conditions with said steam-supply chest by way of said main valve, valve means associated with said endmost chamber and being operable to vary the extent of such communication of the lat- 

